Planetary Radio • Oct 28, 2020

A Deep Dive into Asteroid Bennu With Dante Lauretta

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Nancy Atkinson

Space journalist and author

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Dante Lauretta

OSIRIS-REx Principal Investigator for University of Arizona

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

We are joined by the leader of the OSIRIS-REx mission that sampled an asteroid last week. Dante reveals just how brilliantly successful the encounter was, and describes preparations for the journey back to Earth. Space journalist Nancy Atkinson tells us about Orbilander, a mission that would orbit and then descend to Saturn’s moon Enceladus in a search for life. Space headlines from The Downlink and our weekly visit with Chief Scientist Bruce Betts round out this week’s show.

OSIRIS-REx Sample Collection Location
OSIRIS-REx Sample Collection Location This mosaic of the primary sample collection site for NASA's OSIRIS-REx mission was created with 345 images captured by the spacecraft on 3 March 2020. OSIRIS-REx was 250 meters (820 feet) above the surface at the time. The specific collection site is the relatively rock-free area in the middle. The boulder in the upper-right is 13 meters (45 feet) wide on its longest axis.Image: NASA/Goddard/University of Arizona
Touchdown on asteroid Bennu!
Touchdown on asteroid Bennu! Rocks fly off asteroid Bennu after NASA's OSIRIS-REx spacecraft touched the surface to collect a sample on 20 October 2020. The sample head touched Bennu's surface for 6 seconds while a bottle of nitrogen gas stirred rocks and fine-grained material into a collector. The spacecraft then backed away using its thrusters, as debris filled the camera view.Image: NASA/Goddard/University of Arizona
Bits of Bennu Float from OSIRIS-REx's Sample Head
Bits of Bennu Float from OSIRIS-REx's Sample Head Rocks and dust from asteroid Bennu leak from the TAGSAM sample head aboard NASA's OSIRIS-REx spacecraft on 22 October 2020. The spacecraft collected so much material that the head's Mylar flap did not fully close. The mission team decided to forgo efforts to weigh the sample and instead stow it as quickly as possible.Image: NASA/Goddard/University of Arizona
Enceladus Orbilander
Enceladus Orbilander This artist's concept shows Orbilander in its landed configuration on Saturn's moon Enceladus.Image: Johns Hopkins University Applied Physics Laboratory

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Trivia Contest

This week's prizes:

A Planetary Society KickAsteroid r-r-r-rubber asteroid! (Bennu was already taken.)

This week's question:

As measured by either volume or average diameter, what is the smallest asteroid that has been visited by a spacecraft?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, November 4th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

How many robotic spacecraft have returned samples from the Moon and beyond?


The winner will be revealed next week.

Question from the 14 October space trivia contest:

Who was the original principal investigator on the OSIRIS-REx mission?


Dr. Michael Drake was the original principal investigator for the OSIRIS-REx mission. He also hired Dante Lauretta at the University of Arizona Lunar and Planetary Lab, and became his mentor and friend.


Mat Kaplan: A deep dive into asteroid Bennu with Dante Lauretta, this week on Planetary Radio. Welcome. I'm Matt Kaplan of the Planetary Society with more of the human adventure across our solar system and beyond.

Mat Kaplan: It was just last week that we celebrated the successful collection of material from that asteroid that the OSIRIS-REx spacecraft has been circling for nearly two years. Now we know just how successful that encounter was. Principal investigator Dante Lauretta is here with the exciting and surprising details.

Mat Kaplan: First, though, we'll look to the future and a new proposal for orbiting and landing on Saturn's moon Enceladus. The night sky still beckons, and Bruce Betts answers the call. We'll also congratulate a first time winner of our space trivia contest. The Downlink is the Planetary Society's weekly newsletter. It's a great place to start your own exploration of the solar system, and it's topped this week by an explosive image of that encounter with Bennu. I mean that pretty much literally, as what looks like scores of small fragments explode away from the sample collector on OSIRIS-REx.

Mat Kaplan: Up on Mars, the long-suffering, long-striving mole is entirely beneath the surface. The InSight lander scoop is piling more Martian dirt on top of the hole in what I've just realized may be Mars' first construction project. It may take months, but the InSight team hopes the mole will still dig much deeper to reveal much more about the interior of the red planet.

Mat Kaplan: From Mars to Pluto, where data collected by New Horizons has explained how the planet/not a planet, take your pick, has formed ice caps on its mountains. It's not how they form on Earth, by the way. The men and women living on board the International Space Station can breathe easy again. The small but persistent air leak has been found and plugged. You'll find lots more at

Mat Kaplan: Who doesn't want to fly through those salty plumes emanating from the so-called tiger stripes at the South Pole of Enceladus? Sending a mission to build on the work accomplished by the Cassini spacecraft has come up many times on our show. Well, then how about not just an orbiter, but a lander? I talked a few days ago with space journalist and author Nancy Atkinson about her October 8th article at

Mat Kaplan: Nancy, welcome. It's great to have you on the talk about this terrific article about Orbilander, a mission I hadn't heard of until I read your article. Tell us about this proposal for a trip to Enceladus.

Nancy Atkinson: Right. It's a really fascinating topic. It's part of the decadal survey, an independent assessment that NASA gets, to see the priorities of scientific community and guidance in deciding where to send future missions. There was a group of scientists at Johns Hopkins University that put together an idea, this study to send a mission to Enceladus. Enceladus is just such a fascinating place in our solar system.

Nancy Atkinson: These scientists realize that we probably have one shot in our lifetimes of getting a mission to Enceladus, so why not go for the gold, pull out all the stops, and make it a big flagship mission? Plus, we already know that Enceladus has a habitable environment. It's got a subsurface ocean and the interior of this little moon is just warm enough to keep it liquid water.

Nancy Atkinson: Plus, we have these majestic plumes that we've seen on Cassini images that show us that there's warm hydrothermal vents on the surface. So all evidence points to an environment that's very conducive to life. This mission would cut to the chase and ask the big question: is there life on Enceladus?

Mat Kaplan: I wasn't very far into your great article when I was struck by the similarities between this proposed mission and the Viking orbiters and landers of more than four decades ago that went to Mars. For one thing that they're going to get there and orbit for a while because, as great as Cassini was, we didn't get close up enough images of Enceladus, I guess, to safely put something down on the surface. Then this orbiter will, on its own, turn into a lander.

Nancy Atkinson: Yeah, it's a really fascinating. I think it's the only mission that's ever been designed to be both an orbiter and a lander with one spacecraft. I guess the closest thing we saw to that was what happened just the other day with OSIRIS-REx, where it briefly touched down on the asteroid Bennu. They would plan to orbit Enceladus for approximately 200 days. They'd study the moon with all sorts of instruments. Enceladus gives us this benefit of having these plumes. So they would fly through the plumes repeatedly and collect particles and analyze them on an onboard chemistry lab.

Nancy Atkinson: But the exciting part was while they would be in orbit, they would also be doing reconnaissance. They'd be taking high-resolution pictures of the surface and look for a great landing spot. When it was time, they would pick this spot and they would turn the spacecraft on its side and turn it into a lander. They would try to land, I guess, close to one of these jets or plumes on the surface and capture particles before the particles came back down and hit the ground.

Mat Kaplan: About those instruments that they hope it will carry, I mean, again, this reminded me of Viking, because they will be designed to directly detect life. It's quite a suite of instruments that they're proposing.

Nancy Atkinson: Right. When I was talking to Shannon MacKenzie, who is the principal investigator of this study, she was saying, unfortunately, we don't have one instrument that's called the life detection instrument. They're going to have to combine about six different instruments to really get a great detection. But she said that that's actually great because instead of just getting one dataset, you'd have six different datasets, and that would be a more compelling approach to looking for life.

Mat Kaplan: Absolutely.

Nancy Atkinson: The life detection instruments that they put together, she said that they're basically things that we have available now. So nothing new would have to be developed. That means that these instruments have already been tested or used on previous missions. So that gives them a lot of robustness.

Mat Kaplan: I'm glad you mentioned Shannon MacKenzie of the APL, the Applied Physics Laboratory, the PI for this proposal. Fortunately, your great article also included a link to the mission concept study itself, which is amazingly impressive, so detailed. At the end, it had ...

Mat Kaplan: Well, first of all, it has four pages of acronym definitions, which indicates that this is a real mission, not a proposal for NASA, I guess. But also this long list of members of the science team led by Shannon, which is like a who's who of planetary science and astrobiology.

Mat Kaplan: I was very glad to see some people who were very prominently involved with the Cassini mission, including Linda Spilker, who our audience has heard many times on this show, and the great Carolyn Porco as well, who was with us a year ago.

Nancy Atkinson: Yeah, it really is an impressive list of people who are giving input to this mission. I think that just says what a fascinating place Enceladus is and how keen the scientists are to return there with a big mission to really figure out the big question of if there is life in another part of our solar system.

Mat Kaplan: I've got to bring up one more thing that I pulled from the mission concept study, which is that these scientists expect that when this lander descends to the surface and starts to work, it will be able to detect life that is 500,000 times as scarce as it is in our own planet Earth's oceans. That is just mind-boggling.

Nancy Atkinson: It really is. Yeah, some of the life detection instruments that they have are pretty impressive, mass spectrometers, microscopes, cell sequencers. But then they've got all those remote sensing instruments as well that will really give us a well-rounded picture of Enceladus' environment and hopefully some of its interior aspects as well.

Mat Kaplan: Nancy, thank you for this terrific introduction to the Orbilander mission concept, now under consideration in this brand new decadal study that we'll be following along.

Nancy Atkinson: Thanks a lot, Mat. It was really fun to write about that. It is just a really fascinating topic.

Mat Kaplan: That is space journalist and author Nancy Atkinson who writes for Universe Today, the National Space Society's Ad Astra, and I'm very proud to say the Planetary Society. Her most recent book, and it's terrific, is Eight Years to the Moon: The History of the Apollo Missions, which takes you deep into the contributions of the people who built the Apollo program and the spacecraft that took humans to the moon. Nancy's also a NASA/JPL Solar System Ambassador.

Mat Kaplan: Listen carefully because I'm only going to say this once. Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer, that's OSIRIS-REx, which last week really did prove itself to be solar system royalty. Dante Lauretta is the power behind the throne. The University of Arizona planetary scientist and professor leads the mission as its principal investigator.

Mat Kaplan: As you're about to hear, the successful collection of that sample was not the last step before the spacecraft begins the long journey home. It may be useful to remember that the dirty work was performed beautifully by TAGSAM, the Touch-and-Go Sample Acquisition Mechanism.

Mat Kaplan: By the way, some of you may remember that the asteroid previously known as 1999 RQ36 got the name Bennu in 2013, when the University of Arizona, MIT, and the Planetary Society announced that eight-year-old Mario Puzio's submission had been picked from among 8,000 as the winner of our contest.

Mat Kaplan: Dante, welcome back and congratulations. We listened to the thrilling moment when you and your team got confirmation of contact with Bennu. You worked on this mission for over a decade before that accomplishment. Are you still feeling the high?

Dante Lauretta: Hey, Mat. Absolutely. It's great to be back here. It has been an unbelievable week. It's hard to believe it's only been a week since the TAG event itself, but it exceeded all of our expectations. Absolutely amazing.

Mat Kaplan: Okay. So first that spectacular video of the contact with Bennu, which I think I've probably watched 30, 40 times by now. Then just two days later, confirmation that a sample had been collected with that equally amazing sequence of images. Absolutely spectacular. I just don't have another word for it. Well, I could come up with others, but they'd be words like amazing and stunning.

Dante Lauretta: Absolutely, yes. There's a lot of good news in those images, and we've been analyzing them intently in order to get the approval to go ahead and stow the samples. So there's quite a lot we could cover here, if you want to get into some of the analysis that we did to determine sampling success.

Mat Kaplan: I sure do. But first I want to hear about the news that just came out, well, just minutes really before we're speaking, which is on Monday afternoon. It was just announced that you will be stowing the collector head tomorrow as we speak, October 27th. So no more fist bumps with Bennu?

Dante Lauretta: That's right. We are confident that the TAG event was highly successful and we are in the contingency where we're observing a small amount of mass loss from that TAGSAM device. So we have all agreed, all the way up to Thomas Zurbuchen at NASA headquarters, that the most important thing for us to do is to get that head inside the science canister, which is inside the sample return capsule, which is the safest place for it to be, because that'll contain all the sample all the way through delivery to the surface of the Earth.

Mat Kaplan: You described it on Friday, during that media briefing, as having had almost too much success because of the amount of material that has been collected, and it's actually blocking open this membrane, which is supposed to prevent that escape.

Dante Lauretta: That's right. Our bucket is full and we tried to cram even more stuff in there than it could accommodate, so it literally appears to be overflowing with material.

Mat Kaplan: Just amazing. You're going to be stowing tomorrow. Hopefully that will go well. But you still have to wait until, what, March before you can start the long journey back to Earth?

Dante Lauretta: That's right. Just to be clear, we're going to begin the stow sequencing tomorrow. That's Tuesday, October 27th. We may get stow, at least the TAGSAM had captured into the capture ring, but we're also planning that we may be operating all day Wednesday as well. We're on 24/7 shifts here, triple shifts, in the operations center, because we just want to keep moving forward on this activity until it's complete.

Dante Lauretta: It is a tricky mechanical interface in deep space and we're operating what we call telerobotically. So we're sending commands, the spacecraft is moving the arm or taking images or opening the SRC, whatever we just told it to do, and then we're taking images and we're verifying that on the ground before we proceed to the next step.

Dante Lauretta: It's a very different mode of operation for us and, as you can imagine, painstakingly slow because you have that 36-minute, 37-minute roundtrip light time that you've got to wait for each of those steps to proceed.

Mat Kaplan: So this is not an automated procedure. It's something where it's done command-by-command from the ground via the Deep Space Network.

Dante Lauretta: That's right.

Mat Kaplan: Wow! Is there any concern that that material, some of which is adhering to the exterior of the sample collector, the collector head, that it might interfere with the process of stowing that head?

Dante Lauretta: That is exactly the concern that we have, yeah. We've already identified this in what we call a contingency plan. So the first thing we did was we pulled out the procedure document for stowing sample and we said, "Are we in a new situation, something that we've never thought about or we don't have a contingency plan on the shelf identified?"

Dante Lauretta: We definitely thought that there might be a mechanical interference, that there might be what we thought was something protruding out of the base of TAGSAM that could interfere with that capturing. That's not exactly what the situation is. What we're thinking now is something may fall out of TAGSAM and then on to that capturing. There are a series of latches that will grab the TAGSAM head.

Dante Lauretta: The best analogy I can think of is if you've ever gone skiing, it's kind of like clicking your ski boot into your ski. You've got to get that toe in and then you've got to lock that heel down behind you. If you got a little bit of snow or something in there, it doesn't always go right, especially if you've never worn skis before.

Dante Lauretta: The last time we tried to stow the TAGSAM head into the sample return capsule was here on the ground in Denver, Colorado, in the lab. So we've done it all before. It wasn't easy. It took multiple attempts even here with technicians all around the spacecraft watching everything proceed. So we know it's a very delicate maneuver and that's why we're going to this telerobotic sequential mode of operation.

Mat Kaplan: I sure hope that you get it on the first try. But I'm certainly also glad that you and your team have planned for any contingencies. I hadn't noticed until last week how similar the TAGSAM collector head looks to a much more mundane device: the air filter on my car's engine. Are there other similarities?

Dante Lauretta: That's basically the technology that we're going for. It is an air filter for all practical purposes, with the exception that we went to an airless body, asteroid Bennu, and we had to bring our own air, which we did and which seems to have worked really well. So we're very confident that that filter ... It probably was full when we backed away from the asteroid. Now what we're seeing is the particles appear to have become ... Emitting from the TAGSAM head as a result of moving the arm into those positions to get those camera shots so that we could verify the TAGSAM collection efficiency.

Dante Lauretta: You're in microgravity, you have all of this regolith in this head, and it's fluidized, basically. It behaves like a fluid. I was surprised at the accelerations that the arm and parts on that material, but we looked it up. It's as large as four meters per second squared, which is pretty fast.

Dante Lauretta: So we're moving that stuff around. We're imparting a lot of force to it. I think you just have a diffusion problem where we have a gap in this mylar flap because we tried to cram some big rocks in there apparently at the end. So they're wedging it open a little bit.

Dante Lauretta: We've literally been able to see particles show up over the lip. It's like a random block. They're bouncing around and then they just hit the back of a TAGSAM, and they just come right towards us, towards the camera, and slip out. You could think of it as Brownian motion, all these particles bouncing around inside the TAGSAM head, and every once in a while one of them gets itself on a trajectory where it hits that little gap and slips out.

Mat Kaplan: Physics. It's all physics.

Dante Lauretta: It's all physics and microgravity, which is not always intuitive.

Mat Kaplan: Principal investigator Dante Lauretta and I will dig into the dirty details of the OSIRIS-REx sample collection at Bennu when we get back from this short break.

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Mat Kaplan: Are you confident that if you're able to get it stowed properly tomorrow, maybe Wednesday, you're still going to have a whole bunch of bits of Bennu to bring back to Earth?

Dante Lauretta: We are confident, Mat, that we have a lot of sample in that TAGSAM head. We went through this in great detail, as you can imagine, in order to get the approval to proceed to stow. We had to provide a convincing case that we had a lot of sample and that we had access of material above our level one requirement of 60 grams of material.

Dante Lauretta: There are several reasons that we believe that. First of all, as you mentioned in the beginning, you watched the series of images of TAGSAM making contact with the asteroid surface. We got TAGSAM into as favorable a position as we could have dreamed of.

Dante Lauretta: First of all, there's the two images. There's right before contact and then there's right after contact, before the gas bottle fires. So you can actually see the TAGSAM head imprinting itself on to the asteroid surface.

Dante Lauretta: That is a great shot. We weren't sure we were going to get that, just the way the whole timing of the sequence was going to work. It wasn't guaranteed that we would get a before contact, a post-contact, and then a post-gas firing sequence of images, but we did get that.

Dante Lauretta: We can tell right away that material was disturbed on all sides of the TAGSAM head. Basically, for 360 degrees, you can trace an outline that's on average about one TAGSAM head diameter away from the contact point where the surface just responded through momentum transfer. And so, that means that the head was flush on the surface. There was no gap underneath TAGSAM, which was some of the worst-case scenarios where you propped TAGSAM up and then you just blew the gas out the side.

Dante Lauretta: On top of that, we can see that we actually penetrated about 4.5 centimeters into the regolith before the gas released, which means that we preloaded the head. Basically, all of the material that was underneath TAGSAM got pushed up into the filter even before the gas fired.

Dante Lauretta: And so, we know under those conditions, as soon as you start blowing down that gas, anything that's preloaded is automatically driven into the collection chamber. Because of the approach imaging, we actually counted 35 particles on the surface that were less than two centimeter, which is our collection size, that should now be inside TAGSAM. So we can tell where we hit, and where we hit was very sampleable.

Dante Lauretta: My dream is that when we get the samples back on Earth, we're going to go back to those images and hopefully identify those individual particles that were sitting on the surface of Bennu that are now in our laboratories.

Mat Kaplan: Has anybody started to give those rocks names?

Dante Lauretta: You bet, yeah. The team is very excited. I could tell you as soon as I process all that information, I said, "Okay, we got TAGSAM exactly how we want it to be placed on the surface," and even better because it pushed down into the surface, and the spot we landed on had a lot of material that TAGSAM was capable of ingesting, I knew we had the sample at that point, because our whole verification program for TAGSAM assured that that would be the case.

Dante Lauretta: But on top of that, of course, we got those great images where we see the particles slipping out, but we also see a lot of stuff in TAGSAM itself. First of all, there's five particles that we directly observe that appear to be what's causing the flap to be partially open. Those five particles range in size up to a couple of centimeters. We estimate just those five particles alone probably have a mass of 25 to 28 grams, so about half of our requirement-

Mat Kaplan: Wow!

Dante Lauretta: ... in direct measurement of visible particles in the TAGSAM. We also have a bunch of images of the TAGSAM head when it was empty that we took back in November of 2018, when we first deployed it. Then we have this new image sequence, and that whole screen is opaque to sunlight. There is no sunlight penetrating into the interior of the device.

Dante Lauretta: And so, we did a simple calculation and said, well, if we just blocked the screen, the largest holes that you can see in the shadow are three millimeters. There's a finer mesh on top of those, but those three-millimeter holes, they would make really nice shadows. So we just said if you just covered all of those with three-millimeter particles to block the sunlight, that would take 57 grams of material. You can add that to the 28 grams that are there in visible particles.

Dante Lauretta: Then the area where the flap is pushed back. We can actually see into the container, and we can see a lot of dark, black Bennu-like regolith particles in there, big ones. That's about 17% of the volume of TAGSAM is visible, and we estimate that's about 300 grams of material that we can see in there.

Dante Lauretta: My sense is that the whole filter is filled to that level, i.e., the stuff that we can't see probably also has sample in it as well. I'm confident that we have at least 400 grams of sample that we can see in our imaging data right now. Of course, you have to make assumptions about density, and we've been very conservative with the density estimates.

Dante Lauretta: But I think we have more than that because there's a lot of area of the TAGSAM head that's not visually accessible. Based on the fact of the conditions of collection, it should be equally as full of material as we can see there. So we feel very confident that the few grams that we see leaking out is just slosh of material that's inside that head in much, much higher abundances.

Mat Kaplan: It sure sounds like you hit the jackpot on the first try. I've got to ask you one more thing about the performance of the spacecraft, because I know you're very proud of it. It was exciting as it descended, as we were watching, listening in real time, you'd hear someone say that the margin of error, I forget the exact term, is one meter or a half meter. You really hit the bull's eye, didn't you?

Dante Lauretta: We really did. We definitely hit within a meter of the target location, and I think we've done better than. We actually have a couple different groups reconstructing the contact point, but we're a substantial fraction of a meter at this point to the target point.

Dante Lauretta: Like you said, it was an absolute bull's eye, especially because the area that we touched down on had so many fine-grained particles, which was really what the target was anyway, whether it was the exact coordinate we programmed or just a little bit off to the west. It was a really great location.

Mat Kaplan: You already started to answer this. Just from what you've already been able to see of the sample, this little gift from the problem you've got with that membrane, what has the sample collection already started to tell you about Bennu? Then adding to that, what you've been learning over the last almost two years now, as you've orbited the asteroid with all of your other instruments?

Dante Lauretta: Yeah. The TAG event itself is a great science experiment. One thing we're taking a long look at right now is the surface response, which was really phenomenal. We've done a pretty good job of reconstructing the contact timeline, and so I'll just play that out for you.

Dante Lauretta: Contact time was sensed on the accelerometers on the spacecraft. We had two different ways that we could sense it: either the accelerometer sensed that the spacecraft was slowing down due to resistance by touching the asteroid surface or that TAGSAM arm, which has a compression spring, would have triggered a microswitch. It was definitely the asteroid's surface that we felt at contact, and that set up a timer which opened up the gas bottle one second later.

Dante Lauretta: So we penetrated into Bennu a border 10 centimeters before the gas bottle had fired. Then we see that the gas bottle, as expected, it went from its initial pressure of over 2900 PSI, and I apologize for the imperial units but that's how the engineers report the data to me, 2900 PSI and after five seconds, it was down below 100 PSI, and it was a beautiful exponential decay.

Dante Lauretta: That was almost all the deceleration that the spacecraft received. There was very little resistance from the material. So the TAGSAM exerted a jet force. So six seconds after contact, we were still moving into Bennu's regolith at four centimeters per second. We were still plowing down into the regolith. The back-away burn initiated and the thrusters fired. It took the thrusters another three seconds to reverse our motion.

Dante Lauretta: So we were penetrating for nine seconds. We estimate that we got down to about 49 centimeters depth. So we buried this TAGSAM deep, deep into Bennu regolith. We fired our thrusters and started backing away. It took us another 7.6 seconds to get back above the surface.

Dante Lauretta: So our actual time from sensing contact to where the TAGSAM head was above the location where the surface was originally was 16.6 seconds. Much longer than we thought when we first started reconstructing the event. Bennu behaved as what we call a cohesionless fluid, and we had all these models for how the surface was going to respond.

Dante Lauretta: They ran the whole gamut. It was very challenging as the PI because I commissioned a whole series of studies to tell me exactly this, how far do we think we'll penetrate. I got an answer from three millimeters down to a meter, and everything in between. Then I said, well, it simply depends on the properties of the soil, which we don't know.

Dante Lauretta: So we were definitely at the soft end of those models, which means that the regolith, it has no cohesion between the grains. There's no electrostatic forces or Van der Waals forces or frictional forces that are resisting the grains as they slide past each other. They're cohesionless and they're behaving like a fluid. So it almost rippled, like if you drop a pebble into a pond.

Mat Kaplan: Sure, or when you see a glob of water on the International Space Station that somebody blows on or touches.

Dante Lauretta: Exactly. So the surface really behaved like that. Then the other thing that really surprised us, both in the TAGSAM imaging and soon-to-be-released Navcam imaging, we're in final processing of that product for public release, there was an enormous amount of fine-grained material just under the subsurface.

Dante Lauretta: When we fired those thrusters to back away and we looked at the Navcam, which is a much wider field of view and it's looking off to the side, it doesn't have TAGSAM in its field of view, it just looks like a sand blast moving across Nightingale crater. It's unbelievable.

Dante Lauretta: When we did the remote sensing analysis from the ground using telescopes, we thought the surface would be beach-like and sandy. Then we got there and we saw this rough and rugged rocky surface. Then as soon as we punched below that, that's where all the sand appears to be. It looked like a ton of fine-grained material just underneath the surface of the asteroid. Considering that we went in almost 49 centimeters, that's another reason we think the TAGSAM is just packed full of material, or at least it was as we started to back away.

Mat Kaplan: Absolutely marvelous result. You know who must be terribly envious of you right now is that poor team behind the mole on the InSight lander on Mars, who, thank goodness, are finally having some luck getting below the surface there. If only it had been as easy for them as it's been for TAGSAM.

Dante Lauretta: Yeah. When you're in microgravity, physics are really different and, as we've seen, soil properties are very different. There's a lot more results to come out of the analysis of the dataset. I mean the team is just really getting started in that area.

Mat Kaplan: We're going to have to have you back yet again on the show to talk about some of the other results, maybe around the time you start that journey back to Earth, because I know you're running short of time. You've got a very big step in this mission coming up in the next few hours. I have to ask, though, where do you think you will be in September of 2023, when the sample return capsule enters the atmosphere headed for a, hopefully, none too hard impact in Utah?

Dante Lauretta: I will be right there on the range standing by with the helicopter as soon as that SRC is on the ground and we've determined its location. The recovery team will hop into those helicopters and fly out to the site and begin recovery operations of that amazing sample. So there's still a lot to go in the journey of OSIRIS-REx, but we clearly crossed a major milestone last week.

Mat Kaplan: I've got a quote for you from Administrator Bridenstine, Jim Bridenstine of NASA. "This amazing first for NASA demonstrates how an incredible team from across the country came together and persevered through incredible challenges to expand the boundaries of knowledge. Our industry, academic, and international partners have made it possible to hold a piece of the most ancient solar system in our hands." You want to say anything about those partners?

Dante Lauretta: Yeah. I mean it's all about the team and how amazing this group of people are to work with. I'm at the University of Arizona, and the University of Arizona team was responsible for the science processing and operations. So all of those great data products that we brought back, all of those observations were designed by the crew at U of A.

Dante Lauretta: We're really tightly coupled with our team here at Lockheed Martin in Littleton, Colorado. They built the spacecraft, they operate the spacecraft. The team here is just such a great group of people. They're so much fun to be around, they're so passionate about the mission, and they love the science and they're inspired by it to do the amazing job that we've seen them there.

Dante Lauretta: Then our NASA Goddard Space Flight Center team where the project management is based, as well as flight dynamics leadership, Kinetics Aerospace, which is the group of people that lead the navigation efforts for the program. We had a phenomenal laser altimeter, the OLA instrument from the Canadian Space Agency, which mapped the surface of the asteroid with centimeter scale precision, an amazing dataset that we'll be processing for decades to come.

Dante Lauretta: Really excited to work with our partners in Japan, the JAXA team on the Hayabusa2 mission. We've got a lot of great dialogue going back and forth. We've already done comparative analysis of the Hayabusa2 touchdowns with the OSIRIS-REx sampling event. Of course, their samples are coming back in just a couple short months, and we're all excited to see what they have got from asteroid Ryugu.

Dante Lauretta: That really kicks off the sample analysis program for us, because we've always looked at it not as two programs, but as one continuous sample analysis phase that starts with Hayabusa2 and then receives OSIRIS-REx samples two years later. That just keeps going for five years or so. We have this amazing ability to compare and contrast samples from these two different asteroids.

Dante Lauretta: In the case of Hayabusa2, two different locations on their asteroid. So there's really an amazing period of asteroid science coming up for us here.

Mat Kaplan: Dante, if you can spare one more minute, Bruce Betts offers a space trivia contest question for us each week on the show. He asked listeners last week, this was the question, for the name of the original principal investigator for OSIRIS-REx. Would you like to say something about your mentor?

Dante Lauretta: Yeah. The correct answer is Dr. Michael Drake. He was the director of the Lunar and Planetary Laboratory when I was hired there. We immediately became friends and he was a great mentor for me. First of all, he hired me, which is a huge step, a sign of endorsement there. Then we really worked very closely together for seven years designing and refining this mission concept to the point where, in 2011, NASA awarded us OSIRIS-REx as New Frontiers 3.

Dante Lauretta: Mike passed away in September of that year. It was a crushing blow to me and to the team to lose the leadership like that. But Mike empowered me, he motivated me, and he told me to take this team forward and to bring that sample from Bennu back to the Earth.

Dante Lauretta: I know he's incredibly proud of the team. We all felt like he was there in spirit on Tuesday. He is just as excited to see what those samples are going to be made up as the rest of us. So a lot of this is done for Mike, and I'm eternally grateful for believing in me and for giving me this opportunity.

Mat Kaplan: Thank you, Dante, for that tribute, but also for sharing all of this with the listeners to this show and to fans of the OSIRIS-REx mission around the world. I will let you get back to getting ready to bring those samples back home, where I know there are so many scientists who cannot wait to get their hands on them. Thanks again for taking the time today and best of luck as you seal up that capsule.

Dante Lauretta: Thank you, Mat. If everything goes according to plan, we should be announcing successful stow by Friday at the latest of this week.

Mat Kaplan: That's Dante Lauretta. He is a professor in the Lunar and Planetary Lab at the University of Arizona and principal investigator for the OSIRIS-REx mission that has just successfully collected a sample from an asteroid known as Bennu. He's also the creator of the popular space exploration board games Xtronaut and Downlink and the astronomy game Constellations. I will be back with Bruce Betts and this week's What's Up in just a moment.

Mat Kaplan: Time for What's Up on Planetary Radio, once again bringing you the chief scientist of the Planetary Society, Bruce Betts. Welcome back.

Bruce Betts: Thank you. Good to be back.

Mat Kaplan: From Mel Powell in California. He had yet another response to your request for call signs for me in my Air Force career flying that F-22. I don't know why I didn't think of this. Mel says, "I should be one [1T 00:37:41]." He says, "How often in life have you had to say it's with 1T?" Basically the entire lifetime, Mel. Thank you very much. He also says, "Say hi to Factoid." Hey there, Factoid. What's up?

Bruce Betts: Hello. Well, 1T, there's a blue moon that will not actually be blue on October 31st, Halloween. Blue moon is usually defined as the second full moon in one month. Also that day, Uranus is at opposition, opposite side of the Earth from the Sun, so rising in the east around sunset, setting in the west around sunrise. And so, get a finder chart. You'll need dark skies or some binoculars or a telescope to see it. But now is the best time.

Bruce Betts: We've also got the bright stuff ... Well, I mean the blue moon will definitely be bright. Jupiter and Saturn in the evening sky in the west, southwest. Jupiter looking super bright. Saturn looking yellowish. They'll be getting closer over the next couple of months.

Bruce Betts: Then Mars coming up in the early evening in the east, still look super bright. They will be hanging out next to the getting full moon on October 29th, Thursday. In the predawn east, we've still got super bright Venus. So lots going on.

Mat Kaplan: I was out there last night, saw all of them ... Not Uranus, but the others ... And got out the telescope at the request of my four-year-old grandson. We took a look at the waxing moon.

Bruce Betts: Nice. Wax on. All right. [inaudible 00:39:22] this week in space history, amazingly, 20 years ago, the first crew took occupancy of the International Space Station. There have been people there continuously for 20 years. 20 years that we've not had all of the humans on Earth. On to Random Space Fact.

Mat Kaplan: Can I finish that? Random Space Fact. Random Space Fact. Random Space Fact. Random Space Fact. Random Space Fact.

Bruce Betts: Thank you, Mat. That was delightful.

Mat Kaplan: You're welcome.

Bruce Betts: On Alan Bean's suggestion, the Apollo 12 mission patch has four stars on it, one for each of the three astronauts who flew the mission and one for Clifton Curtis "C.C." Williams Jr, who've been replaced after Williams was killed in a T-38 crash caused by mechanical failure.

Mat Kaplan: Wow! I remember that. Very sad. Nice tribute, though.

Bruce Betts: All right. We move on to the trivia contest. As you know, I asked who was the original principal investigator of the OSIRIS-REx mission. I believe our winner this week is Dante Lauretta from Arizona.

Mat Kaplan: Well, congratulations, Dante. We would send you a rubber asteroid, but you already have a rugged rock and sand one. So to heck with that.

Mat Kaplan: Now we have a real winner too, and it's [Laurel Weller 00:40:53] in the UK, longtime listener, first time winner, who said Dr. Michael J. Drake, who, as we heard from Dante, hired Dante at the University of Arizona, became his mentor and good friend. Laurel, that has gotten you a Planetary Society Kick Asteroid rubber asteroid. Sorry, we can't pull in Bennu for you, but hopefully rubber will do.

Bruce Betts: Maybe in a few years.

Mat Kaplan: From our Poet Laureate, Dave Fairchild in Kansas, "OSIRIS-REx has landed and then taken off again 200 million miles from the place where it began. On Bennu, it descended, grabbed a sample, then said bye. In recognition, Michael Drake, the mission's first PI."

Mat Kaplan: That same Mel Powell who gave me that new call sign of 1T, he said he learned the answer by asking Dante Lauretta on Twitter. Dante, stop that. Don't help people like this.

Mat Kaplan: [Pablo Komisha 00:41:54] in Belarus. Dante talked about the legacy of Michael Drake in a previous episode of the show. We called that The Coming Descent to Asteroid Bennu. It was some months ago. He says, "I love this mission. Last year, I even took part in the CosmoQuest X Citizen Science initiative called Bennu Mappers."

Mat Kaplan: From Stephanie [Retrom 00:42:14] in Arizona, no coincidence as you'll hear, apparently Mike Drake, Michael Drake, was her father's tennis buddy and she says a wonderful, jovial guy.

Mat Kaplan: One more poem from [Gene Lewin 00:42:28] in Washington. "His steadfast and ambitious vision brought forth this sample return mission, a neo-selected R-236 was the destination for OSIRIS-REx," almost. "Working through illness that only a few knew. He would pass before this mission flew. Mike Drake looks on and I'm sure he sees his fellow stalwart success posthumously." Nice tribute.

Bruce Betts: Yeah.

Mat Kaplan: One more of these. From Darren Richie in Washington. "Congratulations to the entire team on a successful touchdown and sample capture. I can't imagine a better tribute to Dr. Drake's audacious mission. Now get home safe." Thank you, Darren. Thank you, everybody. We're ready for another.

Bruce Betts: Speaking of asteroids that aren't made of rubber, as measured by either volume or average diameter, what is the smallest asteroid that has been visited by a spacecraft? Go to

Mat Kaplan: Good one. I don't know this one, so I'm going to depend on all of you to send in the answer and educate me. But you've got to do it, if you want to be eligible for our prize, by Wednesday, November 4th, at 8:00 AM, Pacific time. That prize, well, what else? A Planetary Society Kick Asteroid rubber asteroid. Bruce, we're done.

Bruce Betts: All right, everybody. Go out there and look up the night sky and think about air filters. Thank you and good night.

Mat Kaplan: Like car air filters that look like TAGSAM devices on the ends of long arms on spacecraft that are crammed full of Bennu bits. New breakfast cereal, Bennu bits.

Bruce Betts: Mmm. Yummy.

Mat Kaplan: That's Bruce Betts, the chief scientist at the Planetary Society, who's designing the box, the Bennu bits coming right now as we speak and will again next time on What's Up.

Bruce Betts: Cartoon Mat chowing down on Bennu bits.

Mat Kaplan: Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its members who really dig space exploration. We've got a shovel waiting for you at Mark Hilverda is our associate producer. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Ad astra.